Person: Fernández Pérez, Luis Antonio
Loading...
First Name
Luis Antonio
Last Name
Fernández Pérez
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física Teórica
Area
Física Teórica
Identifiers
100 results
Search Results
Now showing 1 - 10 of 100
Item Finite size effects on measures of critical exponents in d=3 O(N) models(Physics letters B, 1996) Ballesteros, H. G.; Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Muñoz Sudupe, AntonioWe study the critical properties of three-dimensional O(N) models, for N = 2,3,4. Parameterizing the leading correctionsto-scaling for the r] exponent, we obtain a reliable infinite volume extrapolation, incompatible with previous Monte Carlo values, but in agreement with e-expansions. We also measure the critical exponent related with the tensorial magnetization as well as the v exponents and critical couplings.Item Ianus: an adaptive FPGA computer(Computing in science & engineering, 2006) Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Muñoz Sudupe, Antonio; otros, ...Dedicated machines designed for specific computational algorithms can outperform conventional computers by several orders of magnitude. In this note we describe Ianus, a new generation FPGA based machine and its basic features: hardware integration and wide reprogrammability. Our goal is to build a machine that can fully exploit the performance potential of new generation FPGA devices. We also plan a software platform which simplifies its programming, in order to extend its intended range of application to a wide class of interesting and computationally demanding problems. The decision to develop a dedicated processor is a complex one, involving careful assessment of its performance lead, during its expected lifetime, over traditional computers, taking into account their performance increase, as predicted by Moore’s law. We discuss this point in detail.Item Antiferromagnetic O(N) models in four dimensions(Physics letters B, 1998) Ballesteros, H. G.; Carmona, J. M.; Fernández Pérez, Luis Antonio; Tarancón, A.We study the antiferromagnetic O(N). N model in the F_(4) lattice. Monte Carlo simulations are applied for investigating the behavior of the transition for N = 2,3. The numerical results show a first order nature but with a large correlation length. The N = ∞ limit is also considered with analytical methods.Item Off-equilibrium fluctuation-dissipation relations in the 3d Ising spin glass in a magnetic field(Physical review B, 2003) Cruz, A.; Fernández Pérez, Luis Antonio; Jiménez, S.; Ruiz Lorenzo, J. J.; Tarancón, A.We study the fluctuation-dissipation relations for a three dimensional Ising spin glass in a magnetic field both in the high temperature phase as well as in the low temperature one. In the region of times simulated we have found that our results support a picture of the low temperature phase with broken replica symmetry, but a droplet behavior cannot be completely excluded.Item Study of the Coulomb-Higgs transition in the abelian Higgs model(Physics letters B, 1998) Cruz, A.; Íñiguez, D.; Fernández Pérez, Luis Antonio; Muñoz Sudupe, Antonio; Tarancón, A.The order of the Coulomb-Higgs transition in the U (1) -Higgs model with unfrozen modulus of the scalar field is studied. Large lattices (up to 24^4 in one case) and high statistics are used. We fix β = 1.15 and explore specially a region of λ-values where metastability is observed. We study the thermodynamical limit of several observables, in particular, the latent heat, the specific heat, the decrement of the free energy between the maxima and the central minimum of the two-peaked histogram, the Binder cumulant and the displacement of the critical coupling with the lattice size. The results point towards a second order transition for λ ≥ 0.005, while for smaller values of λ the strong metastability growing with the lattice size seems to derive from a first order character.Item Critical behavior in the site-diluted three-dimensional three-state Potts model(Physical review B, 2000) Ballesteros, H. G.; Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Muñoz Sudupe, Antonio; Parisi, G.; Ruiz Lorenzo, J. J.We have studied numerically the effect of quenched site dilution on a weak first-order phase transition in three dimensions. We have simulated the site diluted three-states Potts model studying in detail the secondorder region of its phase diagram. We have found that the n exponent is compatible with the one of the three-dimensional diluted Ising model, whereas the h exponent is definitely different.Item New universality class in three dimensions? The antiferromagnetic RP^(2) model(Physics letters B, 1996) Ballesteros, H. G.; Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Muñoz Sudupe, AntonioWe present the results of a Monte Carlo simulation of the RP^(2) model in three dimensions with negative coupling. We observe a second order phase transition between the disordered phase and an antiferromagnetic, unfrustrated, ordered one. We measure, with a finite size scaling analysis, the thermal exponent, obtaining v = 0.784(g). We have found two magnetic-type relevant operators whose related YJ exponents are 0.038( 2) and 1.338( 8) respectively.Item Critical behavior of the dilute antiferromagnet in a magnetic field(Physical review B, 2011) Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Yllanes, D.We study the critical behavior of the diluted antiferromagnet in a field with the tethered Monte Carlo formalism. We compute the critical exponents (including the elusive hyperscaling violations exponent θ). Our results provide a comprehensive description of the phase transition and clarify the inconsistencies between previous experimental and theoretical work. To do so, our method addresses the usual problems of numerical work (large tunneling barriers and self-averaging violations).Item Proton decay in a nucleus: nonrelativistic treatment of nuclear effects(Physical review D, 1983) Fernández Pérez, Luis Antonio; Fernández Álvarez-Estrada, Ramón; Sánchez Gómez, J. L.In this paper, proton decay in a large nucleus is studied in the framework of SU(5) grand unification theory (GUT). By using a method based upon the Green s-function technique of many-body physics, nuclear effects on spectator and pole terms are computed. The decay width in the nucleus is found to be practically the same as in free space. However, nuclear effects are of considerable importance concerning the positron spectrum. A densitycorrelation expansion is introduced which is useful for carrying out a systematic study of nuclear effects in proton decay in a large nucleus. The method presented here can be easily extended to other GUT's or supersymmetric GUT's.Item First Order Phase Transition in a 3D disordered system(AIP conference proceedings: large scale simulations of complex systems, condensed matter and fusion plasma, 2008) Fernández Pérez, Luis Antonio; Gordillo Guerrero, A.; Martín Mayor, Víctor; Ruiz Lorenzo, J. J.We present a detailed numerical study on the effects of adding quenched impurities to a three dimensional system which in the pure case undergoes a strong first order phase transition (specifically, the ferromagnetic/paramagnetic transition of the site-diluted four states Potts model). We can state that the transition remains first-order in the presence of quenched disorder (a small amount of it) but it turns out to be second order as more impurities are added. A tricritical point, which is studied by means of Finite-Size Scaling, separates the first-order and second-order parts of the critical line. The results were made possible by a new definition of the disorder average that avoids the diverging-variance probability distributions that arise using the standard methodology. We also made use of a recently proposed microcanonical Monte Carlo method in which entropy, instead of free energy, is the basic quantity.